Electrode for cold cathode tube and cold cathode tube employing it

1. An electrode for cold cathode tube, comprising:

a cylindrical sidewall portion;

a bottom portion provided at one end of the cylindrical sidewall portion; and

an opening portion provided at the other end of the cylindrical sidewall portion,

wherein the electrode is formed of a sintered body of a simple substance of a metal selected from tungsten, niobium, tantalum, molybdenum and rhenium, or an alloy containing the metal; and

wherein the electrode satisfies L≧6 (mm), d 2 >d 1 , R≧20 (mm), where L is an overall length of the electrode with respect to an axial direction of the cylindrical sidewall portion, d 1 is an inside diameter of the cylindrical sidewall portion at a portion of ½ of the overall length L d 2 is an inside diameter of the bottom portion, and R is a radius of curvature of an arc of an inner surface of the cylindrical sidewall portion connecting a portion of the inside diameter d 1 and a portion of the inside diameter d 2 .

2. The electrode for cold cathode tube according to claim 1 , wherein a ratio of the d 2 with respect to the d 1 is 1.03 or greater.

3. The electrode for cold cathode tube according to claim 1 ,

wherein the electrode satisfies t 1 >t 2 , where t 1 is a wall thickness of the cylindrical sidewall portion at the portion of L/2 and t 2 is a wall thickness of the cylindrical sidewall portion at the portion of the inside diameter d 2 .

4. The electrode for cold cathode tube according to claim 3 ,

wherein a ratio of the t 1 with respect to the t 2 is not less than 1.2 nor more than 6.0.

5. The electrode for cold cathode tube according to claim 1 ,

wherein a deviation of an outside diameter of the electrode is 0.01 mm or less.

6. The electrode for cold cathode tube according to claim 1 ,

wherein an outside diameter of the electrode is 3 mm or less.

7. The electrode for cold cathode tube according to claim 1 ,

wherein the bottom portion has a chamfered portion formed by performing C-chamfering or R-chamfering on an outer peripheral corner portion thereof, and when an outside diameter of the bottom portion is D (mm), a shape formed by the C-chamfering is C (mm) and a shape formed by the R-chamfering is R 1 (mm), a ratio of the C or the R 1 with respect to the D is not less than 0.08 nor more than 0.40.

8. The electrode for cold cathode tube according to claim 7 , wherein a deviation of the outside diameter of the electrode except the chamfered portion of the bottom portion is 0.01 mm or less.

9. The electrode for cold cathode tube according to claim 1 , wherein the sintered body has an outer peripheral surface on which centerless processing is performed.

10. A cold cathode tube, comprising: a tubular translucent bulb in which a discharge medium is sealed; a phosphor layer provided on an inner wall surface of the tubular translucent bulb; and a pair of electrodes each formed of the electrode for cold cathode tube according to claim 1 and disposed in both end portions of the tubular translucent bulb.

11. An electrode for cold cathode tube, comprising: a cylindrical sidewall portion; a bottom portion provided at one end of the cylindrical sidewall portion; and an opening portion provided at the other end of the cylindrical sidewall portion, wherein the electrode is formed of a sintered body of a simple substance of a metal selected from tungsten, niobium, tantalum, molybdenum and rhenium, or an alloy containing the metal; and wherein the electrode satisfies L≧6 (mm), t 1 >t 2 , R≧20 (mm), where L is an overall length of the electrode with respect to an axial direction of the cylindrical sidewall portion, t 1 is a wall thickness at a portion of ½ of the overall length L (L/2), d 2 is an inside diameter of the bottom portion, t 2 is a wall thickness of the cylindrical sidewall portion at the portion of the inside diameter d 2 , and R is a radius of curvature of an arc of an inner surface of the cylindrical sidewall portion connecting an inside diameter portion of the cylindrical sidewall portion at the portion of L/2 and an inside diameter portion of the bottom portion.

12. The electrode for cold cathode tube according to claim 11 , wherein a ratio of the t 1 with respect to the t 2 is not less than 1.2 nor more than 6.0.

13. The electrode for cold cathode tube according to claim 11 , wherein a deviation of an outside diameter of the electrode is 0.01 mm or less.

14. The electrode for cold cathode tube according to claim 11 , wherein an outside diameter of the electrode is 3 mm or less.

15. The electrode for cold cathode tube according to claim 11 , wherein the bottom portion has a chamfered portion formed by performing C-chamfering or R-chamfering on an outer peripheral corner portion thereof, and when an outside diameter of the bottom portion is D (mm), a shape formed by the C-chamfering is C (mm) and a shape formed by the R-chamfering is R 1 (mm), a ratio of the C or the R 1 with respect to the D is not less than 0.08 nor more than 0.40.

16. The electrode for cold cathode tube according to claim 15 , wherein a deviation of the outside diameter of the electrode except the chamfered portion of the bottom portion is 0.01 mm or less.

17. The electrode for cold cathode tube according to claim 11 , wherein the sintered body has an outer peripheral surface on which centerless processing is performed.

18. A cold cathode tube, comprising: a tubular translucent bulb in which a discharge medium is sealed; a phosphor layer provided on an inner wall surface of the tubular translucent bulb; and a pair of electrodes each formed of the electrode for cold cathode tube according to claim 11 and disposed in both end portions of the tubular translucent bulb.